In cellular communication networks, it is usual to include some kind of admission control function, which regulates the admission of arriving calls into the communication network based on the current load of the network. Typically a call from a new user is admitted if the following condition is satisfied:ρ+Δρ≦ρth  (1)
where ρ is the current load of the cell, Δρ is the estimated load increase that will be caused by admission of the new user's call, and ρth is a threshold parameter. Various methods are known for measuring or estimating the load value ρ for use in call admission decisions.
The threshold ρth represents a trade-off between blocking incoming call requests and the protection of the Quality of Service (QoS) offered to users already connected to the cell. A higher threshold results in fewer blocked calls, but may result in more users sharing the available capacity of the cell, thus reducing the QoS experienced by each connected user.
Typically the threshold ρth is set ‘manually’ by the network operator, which may be on a per-cell basis. However, this is often challenging in practice because the relationship between the load threshold ρth, user QoS and blocking is not simple to predict. An estimate of a suitable threshold value can be determined from analysis and computer simulations of network performance at a base station, but the actual performance is very difficult to predict accurately because it may depend on many factors such as traffic mix, cell size and local radio environment.
Therefore, a method of automatically adjusting ρth would be of considerable benefit, both in terms of simplifying the management of the network and improving operating efficiency and user experience.